This invention relates to communication of information, such as computer data or video, over unshielded twisted-wire pairs (UTP) such as those used for telephone communication within a building.
Referring to FIG. 1, in a typical situation in which a building 100a is coupled to a variety of external information systems, communication within the building may use different wiring networks. The information systems can include public switched telephone network (PSTN) 120, television distribution system 124 and a data network 122. Building 100a can be a single family dwelling or a multiple unit dwelling or office building.
PSTN 120 is coupled to building 100a with one or more UTP cables 121. UTP cables 121 include wire pairs that each provides an outside telephone line to the building. Television distribution system 124 can be a cable or satellite television system which provides multiple channels of television signals over a broadband connection 125, typically a coaxial cable.
Data network 122, such as the Internet, is coupled to building 100a in one of several different ways, providing a high-speed connection (e.g., 1 Mb/s or higher rates). Data network 122 can be coupled through PSTN 120, either using one or more UTP cables 121 to pass data back and forth to building 100a. For instance, the two wire pairs can carry data in a T1 or partial-T1 format in which those wire pairs are used exclusively for data. Alternatively, data network 122 can be coupled to building 100 over some UTP cables 121 using a digital subscriber loop (DSL) signaling technique in which the data communication is passed in a different frequency range than voice telephone communication passing over the same wires.
Data network 122 can also be coupled to building 100a through television distribution system 124. For instance, bi-directional data communication can pass over a cable television distribution system concurrently with television programming.
In building 100a, UTP cables 121 terminate at a telephone interface 132, such as a main wiring block. Similarly, broadband connection 125 terminates at a television interface 152. Data network 122 is coupled to devices in building 100a through a data interface 142. If data network 122 is coupled through PSTN 120, data interface 142 provides an interface appropriate to the type of signaling used (e.g., T1, DSL). If data network 122 is coupled through television distribution system 124, data interface 142 can be a cable modem coupled to broadband connection 125 through television interface 152.
Within building 100a, separate networks are typically used for telephone, data, and television signals. A telephone wiring network 130 couples telephones 134 to telephone interface 132 and to PSTN 120. If no telephone switching equipment is deployed in building 100, telephone wiring network 130 and UTP cables 121 provide a continuous electrical path from each telephone 134 to telephone switch in PSTN 120. Multiple telephones 134 can be connected to the same conductive path when they are extensions of the same telephone line.
A data wiring network 140 couples one or more computers 144 to data network 122 through data interface 142. A common form of data wiring network used within building adheres to one of the Ethernet standards (IEEE STD 802.3, 802.12), such as 10BaseT, 10Base2, 100BaseT4, or 100VG.
In 10BaseT, each data communication paths consisting of two UTP coupling a computer 144 to data interface 142. Communication is at a rate of 10 Mb/s. If more than one computer 144 is connected to data wiring network 140, data wiring network 140 can include a hub (not shown) that is connected to data interface 142 and to each of the computers 144. Each of the computers 144 includes a network interface controller (NIC) that provides an appropriate electrical interface to data wiring network 140. According to the IEEE 802.3 standard, 10BaseT communication paths should be no longer than 330 feet without an intervening hub.
The two UTP which couple two communicating devices consist of one UTP for communication in each direction. The two UTP are not intended for simultaneous communication in both directions. There are however occasions when both devices inadvertently transmit at the same time.
In 10BaseT, a device should not transmit when it is receiving a signal from the other device. As a result, the circumstance where both sides transmit at once only occurs when each side begins a transmission before it receives the signal sent from the opposite end. This creates a condition called a "collision."
When a collision occurs, each device is required to suspend its transmission and wait until they are not receiving a signal. After a period of quiet, each device can attempt to transmit again.
As a result, when a 10BaseT device is transmitting on its outbound wire pair, it must monitor the inbound wire pair only to determine whether or not the other end has sent a signal causing a collision. The device does not need to interpret the information sent in the signal causing the collision.
The signal transmitted by a device to send a binary data stream is a Manchester coding of the binary data stream. A Manchester coding of a data stream is a bi-level signal that has at least one transition per input bit. For 10 Mb/s data stream, the spectrum of the coded data stream extends approximately from 3 MHz to 15 MHz.
In 10Base2, a second 10 Mb/s IEEE 802.3 standard, data communication paths consist of a single transmission line, typically a coaxial cable (e.g., RG-58), coupling a computer 144 to data interface 142. Data wiring network 140 can in this case be arranged in a star configuration or can be run in a daisy-chained arrangement coupling multiple computers 144 to data interface 142. When a 10Base2 device applies signals to the transmission line, it uses a similar Manchester coding used in 10BaseT. The multiple 10Base2 devices receive signals from the same line.
In 10Base2, when two devices transmit at the same time causing a collision, the devices detect the collision by monitoring the DC level of the received signal. When one device transmits, it applies a DC offset to the transmission line. A second device can detect this offset, even while it is transmitting.
The IEEE standard calls for the same transmission levels for 10Base2 and 10BaseT, but the minimum receive level is lower by 6 dB for 10Base2 than for 10BaseT.
Circuitry for converting between the signaling used in the 10BaseT and the 10Base2 standards is available from many vendors. The circuitry is typically called a "media converter." One integrated circuit media converter is a available from Level One Corp., the LXT906 integrated circuit.
In 100 BaseT4, a 100 Mb/s IEEE 802.3 (u) standard, communication is over four UTP. When transmitting, a device sends 33.3 Mb/s on each of three of the four UTP. When receiving, the device receives 33.3 Mb/s on three of the four UTP, including the UTP that it does not use for transmission. The UTP that is not used for transmission is used for collision detection as in the 10BaseT two wire pair standard. Each of the 33.3 Mb/s data stream is block coded resulting in a signal that does not have significant energy in the voice band and extends to approximately 25 MHz.
In 100VG, a 100 Mb/s IEEE 802.12 standard, communication is also over four UTP. When transmitting data, a device sends 25 Mb/s on each of the four UTP. Rather than relying on a collision detection approach, in 100VG, the hub grants permission to transmit to a single device at a time between data transmissions. A non-return-to-zero (NRZ) signaling approach is used to transmit data, resulting in the coded data extending to approximately 15 MHz.
Television wiring network 150 is a coaxial network (e.g., RG-6) which couples each television 154 through television interface 152 to television distribution system 124. Television wiring network typically provides the same broadband signal to multiple televisions 154 which tune to the desired channel. A television 154 can be coupled to television wiring network 150 through a "set-top box" (not shown) which provides tuning capabilities. Some set-top boxes also provide a means of sending control information back to television distribution system 124, for example to order pay-per-view movies or to provide interface television (ITV) functionality.
A computer 146 can also be coupled to data network 122 through a dialed telephone connection using a telephone modem 147 connected to telephone wiring network 130. Telephone modem can use analog signaling within the voice frequency band. Analog telephone modems support relatively low data rates below 56 kb/s. Computer 146 can also be coupled through a cable modem 148 to television wiring network 150.